Senate Democrats are calling on the Labor Department to investigate the Senate's food service vendor to see whether mistreatment of workers has occurred in other areas of the federal government.

The entire Democratic caucus signed onto the letter sent to Labor Secretary Tom Perez on Monday. The call for an audit of the vendor across the federal government follows findings that Restaurant Associates, a subsidiary of Compass Group, re-classified nearly half of Senate food service workers to prevent them from receiving a raise.

"The seriousness of these complaints leads us to question if Compass Group has committed labor law violations at other federal cafeteria facilities," the senators wrote in the letter, provided first to Roll Call. "A DOL-conducted audit of federal cafeteria services contracts with Compass Group and its subsidiaries will help establish whether there is a pattern of behavior by the company."

Sens. Sherrod Brown of Ohio, Minority Leader Harry Reid of Nevada, and Charles E. Schumer of New York, led the effort to gather signatures on the letter. Schumer, who is expected to lead the caucus after Reid retires this year, serves as the ranking member on the Rules and Administration committee, which has oversight over the food service contract.

Senate food workers participated in a number of strikes over the past year to push for higher wages and union representation. The Architect of the Capitol re-negotiated a seven-year contract with Restaurant Associates in December, which was supposed to grant raises to most Senate workers.

But, shortly after the contract took effect, workers raised concerns that their jobs were re-classified at lower wage levels. The Architect of the Capitol, at the request of top Senate Democrats, found that to be accurate for roughly half of the workers.

The Labor Department is already looking into the matter at the Capitol, and now Senate Democrats are asking the agency to investigate the food service vendor in other areas of the federal government.

According to Restaurant Associates' website, the company also operates dining facilities at five Smithsonian locations. The company also runs the Capitol Visitor Center cafeteria.

"This information will be particularly useful as we consider how to respond to the accusations of misclassification and underpayment of workers in the United States Capitol complex," the senators wrote.